This invention relates in general to downhole drilling apparatus and deals more particularly with an improved apparatus and method for installing well casing or removing well casing or a drill rod which may be stuck in a bore hole.
A downhole drilling apparatus of the type with which the present invention is concerned utilizes an air hammer drill mounted at the downhole end of a pipe string to drive a drill bit. The hammer drill includes an axially elongated cylindrical hammer casing or barrel which is mounted on and depends from the lower end of the pipe string. A hammer chuck threadably connected in fixed position to the lower end of the hammer barrel carries an axially vertically reciprocally moveable drill bit having an upwardly facing bit shoulder disposed in opposing relation to a downwardly facing arresting surface on the lower end of the drill chuck. The bit shoulder is normally spaced a substantial distance below the arresting surface, as for example, 2 to 3 inches below the latter surface when the drill bit is in an extended position, wherein it projects downwardly from the chuck. When air under pressure is supplied to the hammer drill with the drill bit in the latter position the hammer remains inoperative causing the pressurized air to be exhausted from the hammer barrel and in a downhole direction through an axially extending passageway in the drill bit. Hammer operation will not commence until the drill bit moves upwardly within the drill chuck and to a retracted position relative to the barrel.
During a normal drilling operation when no substantial resistance is encountered by the drill bit the bit remains in its extended position, the hammer remains inoperative. However, when the drill bit encounters resistance, as, for example, a rock formation, the drill bit moves in an axially upward direction and to a retracted position relative to the hammer barrel. The upward movement of the drill bit causes the upper end of the bit shank to engage and elevate a moving part or piston contained within the hammer barrel to a hammer operating position. When the movable part or piston attains an operating position within the hammer barrel, hammer operation commences and continues until the drill bit passes the obstruction and drops to an extended position which allows the moving part to drop to an inoperative position within and relative to the hammer barrel, thereby arresting hammer operation.
Thus, an air operated hammer which comprises a part of a typical downhole drilling apparatus such as hereinbefore described is adapted to sense an obstruction in its path of its downward movement within a bore hole and operate automatically in response to the sensing of such a resistance.
Heretofore, the aforedescribed hammer action has been employed to aid in well casing installation. A rotary casing adapter connected to an above-ground portion of a drilling apparatus is generally employed to rotate a well casing during casing installation where no substantial resistance is anticipated. However, when it becomes necessary to drive the well casing into the earth the rotary head casing adapter is removed from the apparatus and replaced by a hammer drill of the type hereinbefore generally described. The hammer drill is fitted with a worn drill bit of a conventional type which has been provided with a substantially smooth downwardly facing impacting surface. The hammer drill is lowered to bring the impacting surface into impacting engagement with a horizontally disposed protective plate or like member resting on the exposed upper end of the well casing. The modified drill bit moves upwardly to a retracted position within the hammer barrel causing hammer operation to commence and continue for as long as downward pressure is maintained on the hammer drill relative to the well casing being installed. However, a hammer drill arranged in the aforedescribed manner cannot be employed to apply upwardly directed hammering force to a well casing to remove the casing from the ground because upward movement of the hammer drill renders the tool inoperative.
Accordingly, it is a general aim of the present invention to provide an improved apparatus and method for installing a well casing or removing a well casing or stuck drill rod from the earth and utilizing both rotary and air percussion actions, which actions may be either individually or simultaneously employed.
In accordance with the present invention a well drill casing installation and removal adapter for a hammer drill comprises a unitary structure which includes a cylindrical main body portion having a male hammer chuck thread for mating coengagement with a female hammer chuck thread within a lower end of a hammer drill barrel. An integral diametrically enlarged annular flange portion disposed immediately below the main body portion defines a radially disposed and upwardly facing abutment surface for engaging a downwardly facing end surface on the lower end of the hammer drill barrel. An integral diametrically reduced coaxial cylindrical portion projects upwardly from the main body portion and has a generally radially disposed upwardly facing bearing surface for engaging and holding an axially movable part of the hammer drill in an elevated condition within the hammer drill barrel corresponding to an operative condition of the hammer drill to maintain the hammer drill in its operative condition at all times. A coupling means is provided on the lower end of the adapter for connecting the air hammer to the upper end of a pipe string. A central bore extends coaxially through the adapter and opens through its upper and lower ends. A blow tube is coaxially received within an upper end of the central bore and extends axially upward for some distance beyond the abutment surface at the upper end of the adapter for cooperating with the axially movable part of the hammer drill and provides an air passageway which communicates with the bore and with another air passageway which extends through the movable part of the hammer drill.